# If the core losses are 20 watts at rated load, the core losses at 50% load and 0.8 pf is:?

answers to choose from:

20W, 15W, 12W, 16W

please explain how to do it

### 2 Answers

- BonyLv 51 decade agoFavorite Answer
** The core losses remain at 20Watts. = Answer

The two losses usually considered are,

1. Iron or core losses. These do not change

significantly with load changes. As this is the

type of loss the question asks about, the answer

is that there is no change between full and 50% load.

So 20W losses at FL, still = 20W losses at 50% load.

For related interest,

2. The other losses are copper losses, also

called I²R losses. Note I²R equates to Watts.

There losses relate to the square of the load change.

Assume 60W FL copper losses.

Then at half load copper losses = (0.5)² * 60 = 15Watts.

Then at 1/4 load copper losses = (0.25)² * 60 = 3.75Watts.

Then at 120% load copper losses = (1.2)² * 60 = 86.4Watts.

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- JacyLv 71 decade ago
For a transformer and motors the core losses are constant & independent of load.

Try 20*0.8 = 16 W

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